At the present time, it is no longer a problem to minimize the emission into the atmosphere from a waste incinerator, so that environmental pollution is negligible. To free flue gases from their pollutants, efficient flue gas cleaning plants are known which employ three basic processes; a wet process, a semi-dry process and a dry process. The wet process produces a particularly high degree of cleaning, but necessitates a relatively high expenditure in terms of investment, energy and chemicals.
It is known, from U.S. Pat. No. 4,164,547, to utilise the alkaliniy of flue ash in order to neutralize acidic flue gases. In such a case, flue ash is added, together with calcium oxide or sodium carbonate, to the washing fluid of a flue gas cleaning plant, so that the proportion of chemicals added thereto can be reduced. Efforts are also being made to improve the storage properties.
For the refuse slag, that is to say, for the residues remaining on the hearth or bed of the incinerator, a single wash is generally considered to be sufficient for the removal of easily soluble components, so that they can then be utilised further in, for example, the construction industry. Further processing, such as sieving, may be necessary to achieve this.
Several methods are known for improving the storage properties of the flue ash. In some of them, an additive, such as cement is mixed with the flue ash to cause it to solidify, Hardening of the mixture is achieved by the binding thereof with water. In consequence, a reduced leachability is also achieved. One disadvantage of these methods (except in the Bamberg model) is that an increase in the volume required for the storage thereof is necessitated.
A further possibility of storage is to provide individual containers, however, this is only an interim solution because, in the course of time, even the best container will corrode and the reactivity of the flue ash then reappears.
It is known to treat the flue ash with an acidic solution whereby easily elutable elements, such as cadmium and zinc, can be removed. The ash is then pelleted and re-combusted, whereby organic substances are destroyed and the ash develops properties similar to the slag.